I use Groundskeeper Pro, which for those of you who are not aware, is the Lawn Maintenance version of Blizzard Buster. GK Pro not only incooperates all the features of BB but has a few added bells and whistles too and only costs a few dollars more respectively. The only thing you have to do is add your "snow" services to the services drop down menu for each location and continue to bill your customers as usual, or add your snow customers to the overall list ... it does handle 10,000 customers afterall.
I find this makes the transition thru the seasons easier due to the fact that some of my Lawn Maintenance customers are also snow customers and for billing, it is just easier.
We use quickbooks 2000 wich can be streamlined to fit in perfectly with both snowplowing & outdoor maintenance. As far as route sheets & maps etc. a little creative time on your word processor & you can create custom files to suite your individual needs.Quickbooks is available at most retail computer centers & definetly worth a look.
We have used CLIP for years. Covers all the lawn & snow work as far as scheduling & billing is concerned. We use it in concert with Quickbooks for more detailed billing. There is a QB link available, but we haven't tried that one yet